Field of the Invention
This invention concerns treating solutions for metal printing plates particularly aluminum printing plates to degrease the plates and hydrophilically sensitize the surface.
Metal planographic plates are commercially available items used in the printing and copying industry. Before a metal plate can function as a planographic printing plate it is necessary for the metal surface to be hydrophilically sensitized, that is, for the surface to have a water-wettable coating which can receive an ink-receptive, water-repellant image.
One method of hydrophilically sensitizing a metal surface, particularly an aluminum surface, is by treating the surface with an aqueous alkali metal silicate solution such as a sodium or potassium meta-silicate solution. Such solutions have also been used to clean smudges, and to remove scratches and faint imperfections such as surface scratches from imaged and developed paper printing plates. Other alkaline salts of a strong base and a weak acid in addition to alkali metal silicates have been used in such solutions. See U.S. Pat. No. 3,394,653 entitled NOVEL METHOD OF CLEANING PAPER PLANOGRAPHIC PLATES issued July 30, 1968 to Robert E. Riesberg.
U.S. Pat. No. 3,672,885 issued June 27, 1972 to George M. Ort employed a chelating agent for Fe.sup..sup.+2 or Fe.sup..sup.+3 ions to improve the stability of ferrocyanide against oxidative precipitation. The present invention does not employ ferrocyanide and accordingly does not form stable ferrocyanide containing complexes.